Cyclosporin A is an eleven amino acid, cyclic peptide with clinically proven selective immunoregulatory activity of the fields of organ transplantations (hear, liver, lung, kidney and bone marrow) and auto- immune disorders (uveitus, type 1 diabetes mellitus, rheumatoid arthritis, etc.) Despite this potent and clinically impressive immunosuppressant activity, its use has been restricts by its side effects: nephrotoxicity (major side effect, irreversible fibrosis), hepatotoxicity and neurotoxicity. The mechanisms of expression of these toxicities are not known and the toxicities are only partially controlled by monitoring drug blood levels. Thus the development of a safer analog would greatly expand the clinical utility of this powerful class of immunosuppressants. The long term objective of this proposal is the development of an analog of CsA with higher potency, more selective and/or different immunosuppressant activity and decreased toxicity. The specific aims that are directed towards this long term goal are: the semi-synthesis of a series of olefin analogs of amino acid 1 (a critical amino acid), the in vitro evaluation of the immunosuppressant activity of these analogs, the in vivo evaluation of the nephrotoxicity of the analogs and the correlation of the latter two activities with the 3 dimensional solution structure of the analogs as determined by NMR spectroscopy. The procedure for the semi-synthesis of the CsA analogs has already been developed and involves an oxidative cleavage of the double band in residue 1 followed by olefination. The evaluation of the in vitro immunosuppressant activities will be accomplished by known procedures involving inhibition of IL-2 production, inhibition of thymocyte proliferation, competitive binding (CsA vs analog) to cyclophilin (putative CsA receptor) and analog recognition by CsA MAB. The evaluation of nephrotoxicity will be done in the previously used rat model by evaluation of kidney function (GFR,BUN and creatinine levels) and kidney morphology (light microscopy: cell proliferation, tubule cell vacuolization, tubule atrophification and fibrosis). These latter two characteristics will be correlated to the 3 dimensional structure of the analogs which will be determined by the use of 1 and 2 dimensional NMR spectroscopy techniques and the 3 dimensional structure analysis program DSPACE. The results of these studies will lead to the development of structure-activity relationships which will lead to the development of safer, more powerful CsA immunosuppressant analogs.